Introduction

• The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life.
• The cell was discovered by Robert Hooke in 1665.
• The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

Anatomy of cell

On the basis of the absence of well-defined nucleus, living organisms were earlier classified into two groups by molecular biologist viz.

• Prokaryotes: Cells not having well defined nucleus as in bacteria and blue green algae.
• Eukaryotes: Included remaining type of organisms having well-organized nucleus.